Abstract:
Nonlinear static analysis has recently become one of the most commonly used analysis
procedures for design and seismic performance evaluation of buildings, due to its simplicity and
practicality. One of the most important reasons seismic evaluation of an existing building may be
needed, is because the structure that is being evaluated has not been designed in compliance to
the modern building codes, or an upgrade has been made to the existing codes of design.
In this study, a pushover analysis is performed for an existing reinforced concrete frame building,
built in Albania around the year 1999. The building is designed based on the latest Albanian code
for seismic design, KTP-1989. The code has not been revised since the time it was put into
practice, but it is expected to be subjected to certain alterations in the near future, with the
purpose of adopting the Eurocode requirements.
Eleven theoretical cases are defined, taking into consideration the minimum and maximum
values of steel percentage in the reinforced concrete members, several combinations of limit
values (min, max) for steel and concrete strength based on the code, different plastic hinge
properties, and the implementation of steel yield strengths obtained by tensile test results of
steel commonly used for reinforced concrete buildings in Albania.
The pushover analysis is carried out in Sap2000. Observations show that an increase in steel
percentage, or an increase in concrete and steel strength results in significantly higher overall
capacity of the structure. Also, a combination of low concrete strength with high steel strength,
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results in a higher overall capacity, than a high concrete-low steel combination. Furthermore, the
analysis shows that the user-defined hinge model is more successful in capturing the nonlinear
behavior of the structure than the default hinge model.
The pushover analysis of the frame with steel obtained from the tensile tests, indicates that,
although the building is able to withstand the level of design earthquake, the examination of test
results shows that there isn’t yet a standard and a control over the steel used for reinforced
concrete structures.
